changed mrb_str_size and mrb_str_bytesize comments.
Fix String#succ. "-".succ should be "."
Fix String#succ. "-a-".succ should be "-b-"
"-a-a-".succ should be "-a-b-"
Merge pull request #2523 from kkkkkt/changed_string_method_comment

changed mrb_str_size and mrb_str_bytesize comments.
Merge pull request #2524 from mattn/fix-succ

Fix String#succ. "-".succ should be "."
fix build when neither src nor mrblib directory exists.
Merge pull request #2526 from iij/pr-test-only-gem

fix build when neither src nor mrblib directory exists.
mrb_str_bytesize is a carbon copy of mrb_str_size.  remove it.

mruby core does not support any character encodings but ASCII.
Merge pull request #2527 from iij/pr-remove-mrb_str_bytesize

mrb_str_bytesize is a carbon copy of mrb_str_size.  remove it.
changed some string method's mrb-aspec
Merge pull request #2529 from kkkkkt/change-string-method-mrb-aspec

changed some string method's mrb-aspec
refactor mrb_hash_shift, num_pow, flo_eq, flo_finite_p method
Merge pull request #2531 from kkkkkt/refactor-numeric-hash-method

refactor mrb_hash_shift, num_pow, flo_eq, flo_finite_p method
remove unnecessary mrb_float casting; ref #2531
add write barrier when iv is copied
need to add space for receiver to proc env; fix #2525
Remove some roundoff from mrb_flo_to_str
Merge pull request #2532 from chasonr/float-to-string

Remove some roundoff from mrb_flo_to_str
Refactor flo_mod func in numeric.c